Antifoggants and stabilizers for photographic silver halide emulsion



United States Patent 3,042,521 ANTIFOGGANTS AND STABILIZERS FOR PHOT0- GRAPHIC SILVER HALIDE EMULSION Fritz Dersch and Emil B. Ranch, Binghamton, N.Y., assignors to General Aniline 8: Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 26, 1957, Ser. No. 705,151 6 Claims. (Cl. 96-66) The present invention relates to the use of anti-fogging and stabilizing agents for photographic silver halide emul' sions and, more particularly, to the use of sulfoalkyl-Z- thiazolyland oxazolylthio ethers, their salts and esters for such purpose.

It is known that light-sensitive emulsions such as gelatino silver halide emulsions have a tendency to fog. This fog may be due to a number of causes as, for example, excessive ripening of the emulsion, storage of the film at elevated temperatures and humidity or prolonged development of the exposed emulsion.

Benzthiazole and its derivatives, such as Z-mercaptobenzthiazole, have been recommended as being etfective in preventing any increase in fog through stabilizing or controlling the keeping qualities of light-sensitive silver halide emulsions. Although these compounds have the ability to reduce fog tendencies and to improve stability, they are deficient in that they lower the sensitivity of the emulsions and in many cases reduce optical and dye sensitivity.

We have now found that sulfoalkyl-Z-thiazolylthio ethers and the corresponding oxazolylthio ethers, their salts and esters are not only excellent stabilizers or antifogging agents for light-sensitive silver halide emulsions but, in addition, they have the faculty of performing this function without lowering the sensitivity of the emulsion with which they are associated or without reducing the sensitivity of the emulsion to light of longer wave length attributable to the presence of sensitizing dyes.

The use of such compounds to inhibit fog and to stabilize silver halide emulsions either by locating the same in the emulsion or in layers adjacent thereto or in processing baths for the emulsion constitutes the purposes and objects of the present invention.

The antifoggants, the use of which is contemplated herein, may be represented by the following formula:

wherein R is hydrogen, an aliphatic radical such as 'alkyl, i.e., methyl, ethyl, propyl, butyl, amyl and the like; hydroxyalkyl, i.e., hydroxymethyl, hydroxyethyl and the like; carboxyalkyl, i.e., carboxymethyl, carboxyethyl and the like; aryl such as phenyl, toluyl, naphthyl, carboxyphenyl, sulfophenyl and the like; aralkyl such as benzyl or a salt-forming group such as sodium, potassium, ammonium, silver or the like; R is hydrogen, alkyl as above, aryl as above or carboxyalkyl as above or both Rs together form a fused-on aromatic ring such as benzo or naphtho, said benzo or naphtho ring if desired bearing a substituent such as halogen, i.e., chloro, bromo or the like; alkoxy, i.e., methoxy, ethoxy or the like; alkyl, i.e., methyl, ethyl, propyl or the like; aryl, i.e., phenyl, toluyl or the like; su-lfo, carboxy, nitro or the like; Y is oxygen or sulfur and n is a whole number of from 2 to 3.

Examples of compounds within the ambit of such formula which we have found to be etfective are:

(1) p-(2-benzthiazolyl)mercaptoethanesulfonic acid and its sodium, potassium, ammonium or silver salt 3,042,521 Patented July 3, 1962 (2) 7 (2 benzthiazolyl)mercaptopropanesulfonic acid and its sodium, potassium or silver salt (3) The methyl, ethyl or phenyl ester of [B-(Z-benzthiazolyl)mercaptoethanesulfonic acid (4) The methyl or phenyl ester of 'y-(2-benzthiazolyl) mercaptopropanesulfonic acid (5) p (2 5' sulfobenzthiazolyl)mercaptoethanesulfonic acid sodium salt (6) ,8 (2 5 chlorobenzthiazolyl)mercaptoethanesulfonic acid sodium salt (7) 7 (2 5 methoxybenzthiazolyl)mercaptopropanesulfonic acid (8) B (2 5' methylbenzthiazolyl)mercaptoethanesulfonic acid (9) 'y (2 5' phenylbenzthiazolyl)mercaptopropanesulfonic acid (10) B (2 thiazolyl)mercaptoethanesulfonic acid and its sodium, potassium or silver salt (11) p (2 4' methoxythiazolyl)mercaptoethanesulfonic acid (12) B (2 a naphthiazolyl)mercaptoethanesulfonic acid (13) 3 (2 benzoxazolyl)mercaptoethanesulfonic acid and its sodium, potassium or silver salt (14) (2 benzoxazolyl)mercaptopropanesulfonic acid and the methyl, ethyl or phenyl ester thereof.

(15) 13- (2 5' chlorobenzoxazolyl)mercaptoethanesulfonic acid (16) B (2 oxazolyl)mercaptoethanesulfonic acid and the sodium, potassium or silver salt thereof (17) 7 (2 oxazolyl)mercaptopropanesulfonic acid sodium salt acid in the presence of an acid binding agent such as sodium hydroxide, pyridine or the like.

After allowing the mixture to stand overnight, the product is filtered and dried. It may be recrystallized from ethanol and dried at room temperature.

The product was obtained in this procedure in the form of its alkali metal salt. If the free acid be desired, it is obtained by passing a solution of the alkali metal salt through an anion exchange resin such as those described in US. Patent 2,732,352 or 2,591,573.

If the esters are desired they may be produced in the conventional manner by refluxing the free acid with the desired alcohol or phenol in the presence of hydrochloric acid.

Beneficial effects and fog reduction are obtained when solutions of the aforementioned compounds are incorporated in the silver halide emulsions as ripening finals" or as coating finals. Ripening finals are added during the ripening or the sensitivity increasing stage of the emulsion making process. Such additions may be made v before, during or after the decomposition of the soluble silver salt such as silver nitrate by means of soluble hal- 0 centration of 10 to 500 mg. per .4 mol of silver halide.

The concentration used depends very much on the type of emulsion employed and it is advisable to determine the optimum concentration from case to case.

In some instances, it is advantageous to apply the antifoggant in layers adjacent to the emulsion, that is, in a separate undercoating layer or in the anti-abrasion gelatin surface. In other instances, the desired result may be obtained by adding the antifoggant to one or several of the processing baths, i.e., developer or fixer for the involved emulsion.

The aforesaid antifoggants and stabilizers may be employed in connection with any type of photographic emulsion, e.g., non-sensitized, orthochromatic, panchromatic, X-ray emulsions, paper emulsions, color emulsions or the like. They may be used in combination with other known antifoggants and stabilizers, reductionand metaland noble metal sensitizers or in combination with hydroxypolyethenoxy derivatives, i.e., those obtained by reacting ethyleneoxide with an alcohol, phenol, amine or the like (see US. Patent 1,970,578).

The invention is illustrated by the following examples but it is to be understood that the invention is not to be restricted thereto.

Example I A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide was prepared in a conventional manner and brought up to its maximum light sensitivity. It was then readied for coating, finals were added such as sensitizing dyes, and hardening agents. A 1% solution of the sodium salt of fi-(Z-benzthiazolyhmercaptoethanesulfonic acid in water was prepared and added to the emulsion as an antifoggant and stabilizer. The emulsion samples contained about .4 mol of silver halide. The so prepared emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these coatings were then exposed in a type IIB sensitometer and developed in a developer of the following composition:

Metol grams 1.5 Sodium sulfite, anhydrous do 45 Sodium bisulfite ..do 1 Hydnoquinone 3 Sodium carbonate, monohydrated do 6 Potassium bromide ..do .8 Water to make liter-.. 1

Fog Oven Fog Quantity otCompound Added Relative at 12' at 6 Speed Develop Development ment The ,8 (2 -benzthiazolyl)mercaptoethanesulfonic acid sodium salt was prepared as follows:

8.3 grams of Z-mercaptobenzthiazole were dissolved in 25 cc. of water containing 2 grams of sodium hydroxide. 12 grams of technical 2-bromoethanesulfonic acid sodium salt dissolved in 50 cc. of water were added in one portion. After refluxing for 1.5 hours the clear solution was allowed to stand at room temperature overnight. The desired product was filtered off and weighed 14.3 grams after drying. The crude product melted at approximately 210 C. It was recrystallized from 80% ethanol and dried at room temperature for 4 hours. The product has the following formula:

Example 11 4 that the sodium salt of p-(2-benzthiazolyl)-mercaptoethanesulfonic acid was replaced by an equivalent quantity of fl(2-benzoxazolyl)mercaptoethanesulfonic acid sodium salt.

The benzoxazolyl derivates was prepared in the same fashion as the benzthiazolyl derivate excepting that the Z-mercaptobenzthiazole was replaced by an equivalent quantity of Z-mercaptobenzoxazole.

The results obtained with the benzoxazole derivative were similar to the results obtained in Example I.

Example III The procedure was the same as in Example I excepting that there was employed as the antifoggant -(2-benzthiazolyl)-mercaptopropanesulfonic acid. The results were similar to those of Example I.

The antifoggant of this example was prepared in the same manner as that of Example I excepting that the 2-bromoethanesulfonic acid sodium salt was replaced by an equivalent quantity of 'y-bromopropanesulfonic acid sodium salt.

Example IV Exposed samples of a photographic film were developed for twelve minutes at 65 F. in a standard metolhydroquinone developer. Two tests were made, one with the normal developing solution and one with a developer containing mgs. of the sodium salt of fl-(2-benzthiazolyl)mercaptoethanesulfonic acid per one liter of developer. Sensitometric strips, developed in the normal developer (control) for twelve minutes showed a fog of .30, whereas those strips which were developed in the developer containing the antifoggant had a fog of .20.

Example V The procedure was the same as in Example IV excepting that the )3-(2-benzthiazolyl)mercaptoethanesulfonic acid was replaced by an equivalent quantity of p-(2-benzoxazolyl)mercaptoethanesulfonic acid. The results were substantially the same as those obtained in Example IV.

Various modifications of the invention will occur to persons skilled in the art. Thus, it is evident that in lieu of the antifoggants of the examples any of the antifoggants specifically mentioned may be employed. We, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. A light-sensitive photographic material comprising a base and a light-sensitive silver halide emulsion thereon, said light-sensitive material containing as an antifoggant a compound selected from the class consisting of those of the following formulae:

wherein R is selected from the class consisting of hydrogen, alkyl, hydroxylalkyl, carboxyalkyl, aryl, aralkyl and a cation; R is selected from the class consisting of hydrogen, alkyl, aryl and carboxyalkyl; X represents the atoms necessary to complete a nucleus selected from the class consisting of those of the benzene and naphthalene series; Y is selected from the class consisting of oxygen and sulfur and n is a whole number of from 2 to 3 2. The article as defined in claim 1 wherein said antifoggant is located in the silver halide emulsion.

3. The article as defined in claim 1 wherein said antifoggant is located in a layer adjacent to said silver halide emulsion.

4. A light-sensitive photographic material comprising a base with a light-sensitive silver halide emulsion thereon, said emulsion containing as an antifoggant the compound B-(Z-benzthiazolyl)mercaptoethanesulfonic acid sodium salt of the formula:

5. The process of minimizing and preventing fog in light-sensitive silver halide materials comprising a base having a light-sensitive silver halide emulsion thereon which comprises exposing said emulsion and developing the same in the presence of an antifoggant and stabilizer selected from the class consisting of those of the following formulae:

wherein R is selected from the class consisting of hydrogen, an alkyl, hydroxyalkyl, carboxyalkyl, aryl, aralkyl and a cation; R is selected from the class consisting of 1 References Cited in the file of this patent UNITED STATES PATENTS 2,186,849 Wilmanns et al. Jan. 9, 1940 2,490,745 Carroll et al. Dec. 6, 1949 2,697,100 Knott Dec, 14, 1954 2,819,965 Murray et al. Jan. 14, 1958 2,915,395 Popeck et al Dec. 1, 1959 FOREIGN PATENTS 973,727 France Sept. 20, 1950 

5. THE PROCESS OF MINIMIZING AND PREVENTING FOG IN LIGHT-SENSITIVE SILVER HALIDE MATERIALS COMPRISING A BASE HAVING A LIGHT-SENSITIVE SILVER HALIDE EMULSION THEREON WHICH COMPRISES EXPOSING SAID EMULSION AND DEVELOPING THE SAME IN THE PRESENCE OF AN ANTIFOGGANT AND STABILIZER SELECTED FROM THE CLASS CONSISTING OF THOSE OF THE FOLLOWING FORMULAE: 